Tropical Storm Erika's future highly uncertain

The tropical wave we were calling Invest 94 finally decided to stop dawdling and become Tropical Storm Erika yesterday. However, Erika seems intent upon keeping us guessing about its intentions, as the storm's future track and intensity remain highly uncertain. After a modest burst of intensification to a 60 mph tropical storm last night, Erika has become quite disorganized this morning. The Hurricane Hunters found multiple swirling centers inside Erika early this morning, and the main center took a jump to the southwest to relocate itself under a batch of intense thunderstorms. The exact location and path of Erika remain uncertain at this point, and it is possible the storm will have another center relocation later today. Wind shear analyses from the University of Wisconsin diagnose a moderate 10 - 15 knots of shear over Erika, a decrease from yesterday. SSTs are warm, 29°C. Why, then, is Erika so disorganized? The trouble with the various wind shear analyses we use is that they take a crude average of winds over a thick layer to arrive at an average shear, and this large-scale average shear does not capture thin layers of shear that can dramatically affect a tropical cyclone. Upper air data from Guadeloupe and Saint Martin from last night show a complicated shear pattern in Erika's region, with 30 knot winds out of the south to southwest at 200 mb height, nearly calm winds between 300 - 500 mb, and northeasterly winds of 10 - 20 knots from the surface to 500 mb. Some extremely dry air with humidities near 10% was present in a thin layer near 600 mb on the Guadeloupe sounding, so dry air from the Saharan Air Layer is probably being injected by a northeasterly jet of wind into the core of Erika. The shear of 30 knots at the top of the storm is ripping away the heat and moisture Erika's thunderstorms are lifting there, and the result of the shear and dry air is a very disorganized tropical storm.

Erika is embedded in a weak steering current pattern, and the future track of the storm will depend greatly upon how strong the storm gets over the next few days. A stronger Erika will extend higher into the atmosphere and be steered more to the northwest by upper-level winds. A weaker Erika will be steered more by the low-level winds, which will keep the storm on a more westerly track. Given the complicated nature of the wind shear pattern in the region, it is difficult to forecast how strong Erika will get. Virtually anything can happen over the next five days, from dissipation (as forecast by the ECMWF model) to intensification to a Category 3 hurricane (as forecast by the HWRF model). Large-scale wind shear is expected to increase to 20 - 25 knots between 3 - 4 days from now, so Erika will have to deal with an increasing amount of adversity. The storm is a long-term threat to the Bahamas and U.S. East Coast, particularly if the storm stays weak over the next three days. Potential landfall solutions from the models range from Florida on Tuesday (GFS model) to North Carolina on Wednesday (Canadian model).

Figure 1. Morning image of Tropical Storm Erika, showing a false center over Guadaloupe--one of several surface swirls the Hurricane Hunters found in the storm.

Elsewhere in the tropicsThe tropical wave off the coast of Africa we were watching on NHC's Tropical Weather Outlook as having a low chance of developing into a tropical depression has been done in by the dry air of the Sahara, and is no longer a threat to develop. A large and well-organized tropical wave will emerge from the coast of Africa on Thursday, and several of the models develop this low into a tropical depression by early next week. The remains of an old cold front off the coast of North Carolina could serve as a breeding ground for some tropical development Friday or Saturday, but anything that forms in this region would get swept quickly northeastward into New England by Sunday without enough time to become a tropical depression.

Hurricane Jimena nears BajaHurricane Jimena has steadily weakened over the past day, and is now down to a Category 2 hurricane with 105 mph winds. The storm should continue to steadily weaken over the next 24 hours as the waters under the hurricane cool from 28°C to 27°C. Jimena is battering a relatively unpopulated stretch of coast, and largely spared the tourist mecca on the southern tip of Baja. It now appears unlikely that moisture from Jimena will reach the Southwestern U.S., and the hurricane appears poised to stall out over Baja and die five days from now.

Baja's hurricane historyThe most powerful hurricane on record to hit the west coast of Baja occurred last year, when Hurricane Norbert made landfall on the central Baja coast with sustained winds of 105 mph (Category 2) . Norbert's central pressure of 956 mb at landfall made it the 3rd strongest hurricane to hit the Pacific coast of Mexico since record keeping began in 1949. Norbert killed eight, knocked out power to 20,000 homes, and damaged or destroyed 40% of the homes on the islands of Margarita and Magdalena. Norbert crossed the Baja Peninsula and made landfall on Mainland Mexico as a Category 1 hurricane with 85 mph winds.

Only two major hurricanes have made landfall on Baja since record keeping began in 1949. Both hurricanes hit the east (Gulf of California) side of Baja. The first was Hurricane Olivia of 1967. Olivia made landfall on October 13, 1967 as a Category 3 hurricane with 125 mph winds. Due to its small size and the unpopulated region of coast it hit, damage was minimal. The second major hurricane was Hurricane Kiko, which made landfall on August 27, 1989, as a Category 3 hurricane with winds of 115 mph (minimal Category 3). Kiko was a small hurricane and hit a relatively unpopulated area, resulting in no loss of life and only scattered reports of damage.

Figure 3. A plot of all the major hurricanes to pass within 200 miles of Mexico's Baja Peninsula since 1949. Image credit: NOAA Coastal Services Center.

California fire webcamsAs I discussed in yesterday morning's post, you can use our wundermap for Los Angeles with the fire layer turned on to see where the fire and smoke are located, and track the temperatures and winds during today's air pollution event. We also have two webcams with views of the fire: Altadena and Tujunga.

I'll have an update by 4pm this afternoon, when the data from the next hurricane hunter flight into Erika will be available.

Quoting tornadodude:Thank you everyone for making this blog much more enjoyable today! I'm impressed with the knowledge that you guys have displayed today, and also the good sense of humor! :) keep it real, but fun,im off to my EAS class and lab =D so behave everyone,jk ,-Matt

Quoting TreasureCoastFl:Wind shear is often the most critical factor controlling hurricane formation and destruction. In general, wind shear refers to any change in wind speed or direction along a straight line. In the case of hurricanes, wind shear is important primarily in the vertical direction--from the surface to the top of the troposphere. The troposphere is the region of the atmosphere that our active weather is confined to, and extends up to about 40,000 feet altitude (a pressure of about 200 mb) in the tropics in summer. Hurricanes fill the entire vertical extent of the troposphere, and are steered by the average wind through this layer. When one hears the phrase, "wind shear is 20 knots over the hurricane", this typically refers to the difference in wind speed between 200 mb (the top of the troposphere, 40,000 feet altitude) and a layer where a pressure of 850 mb is found--about 5,000 feet above the surface. This wind shear is computed over a large area--a circle of 700 miles in diameter centered on the hurricane is one technique used. This 200-850 mb wind shear is a crude measure of the actual wind shear a storm experiences, since only changes in wind speed--not wind direction--are considered. Furthermore, the computed shear does not consider any smaller scale changes that may occur within this large volume of the atmosphere. For example, it is common to find a strong jet of wind at about 600 mb blowing along the edge of the Saharan Air Layer (SAL)--that area of dry, dusty air that frequently lies to the north of developing tropical cyclones in the mid-Atlantic. This jet will create significant wind shear that will not show up on the standard 200-850 mb wind shear plots. Since upper-air measurements are very sparse over the open ocean, wind shear that is invisible on 200-850 mb wind shear analysis charts will often unexpectedly kill or weaken a developing tropical cyclone.

Another point to make that complicates shear...

The system itself changes wind patterns within these layers. A large hurricane like Bill is like a giant rotating cylinder...and doesn't much feel low/mid level shear because it is the determining force for wind at these levels.

Higher up in the atmosphere, large (synoptic) scale patters drive the flow. Yeah, a hurricane can have some influence developing an anti-cyclone...but large troughs and the westerlies break down the storm very effectively.

Quoting TreasureCoastFl:That happened to me with the sonic boom from the shuttle came in to land.

Wasn't it cool? I was at my mom's in Mississippi when I experienced a sonic boom from a space shuttle. I ran outside to see what the heck happened, and then saw on the news that the space shuttle just returned. It was soooo cool!

Thank you everyone for making this blog much more enjoyable today! I'm impressed with the knowledge that you guys have displayed today, and also the good sense of humor! :) keep it real, but fun,im off to my EAS class and lab =D so behave everyone,jk ,-Matt

Based on what I have seen from the models over the past 24 hours, I still believe that *IF* Erika survives, the most likely CONUS landfall would be in the Carolinas, otherwise, I see it going up the Eastern seaboard to Canada or out to sea...period. I understand Florida and the GoM have had a "boring" hurricane season thus far, but that is no reason to develop a bias toward Florida/GoM storms. THUS FAR, the models and this season's history dont support it.

UPDATE…SUN-TUE…HAVE MADE NO CHANGES TO THE EXTENDED AT THIS TIME. MUCH UNCERTAINTY EXISTS WITH EVENTUAL TRACK OF ERIKA. HAVE UNDERCUT WNAWAVE BY 1-2FT FROM LATE WEEK ONWARD AS WINDS DON`T SEEM TO JUSTIFY 4-5FT SEAS OVER THE MARINE AREA…AND THERE DOESN`T SEEM TO BE A DECENT SWELL GENERATING MECHANISM FOR THE TIME BEING. FCST GETS MORE UNCERTAIN EARLY NEXT WEEK ONCE T.S. “ERIKA” GAINS A BIT MORE LATITUDE. COULD SEE A LITTLE SWELL COMPONENT…HOWEVER MOST OF IT WILL BE BLOCKED/DAMPENED OUT BY THE BAHAMA CHAIN UNTIL PAST DAY 5. HAVE ALLOWED SEAS TO RISE TO 3-4FT BY NEXT WED…BUT CONFIDENCE IN THE FCST IN RATHER LOW AT THAT TIME.

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Quoting TreasureCoastFl:Wind shear is often the most critical factor controlling hurricane formation and destruction. In general, wind shear refers to any change in wind speed or direction along a straight line. In the case of hurricanes, wind shear is important primarily in the vertical direction--from the surface to the top of the troposphere. The troposphere is the region of the atmosphere that our active weather is confined to, and extends up to about 40,000 feet altitude (a pressure of about 200 mb) in the tropics in summer. Hurricanes fill the entire vertical extent of the troposphere, and are steered by the average wind through this layer. When one hears the phrase, "wind shear is 20 knots over the hurricane", this typically refers to the difference in wind speed between 200 mb (the top of the troposphere, 40,000 feet altitude) and a layer where a pressure of 850 mb is found--about 5,000 feet above the surface. This wind shear is computed over a large area--a circle of 700 miles in diameter centered on the hurricane is one technique used. This 200-850 mb wind shear is a crude measure of the actual wind shear a storm experiences, since only changes in wind speed--not wind direction--are considered. Furthermore, the computed shear does not consider any smaller scale changes that may occur within this large volume of the atmosphere. For example, it is common to find a strong jet of wind at about 600 mb blowing along the edge of the Saharan Air Layer (SAL)--that area of dry, dusty air that frequently lies to the north of developing tropical cyclones in the mid-Atlantic. This jet will create significant wind shear that will not show up on the standard 200-850 mb wind shear plots. Since upper-air measurements are very sparse over the open ocean, wind shear that is invisible on 200-850 mb wind shear analysis charts will often unexpectedly kill or weaken a developing tropical cyclone.

Quoting jpsb:I've been telling my friends for months, "Watch out for this winter, it is going to be a cold one". A cool front this strong in the middle of summer in Texas! Yikes, been stocking up on firewood, hope we don't get any hard freezes or big snow storms but I am expecting that this winter. I free sorry for the folks up north hope they are prepared.

There's a local met in KC who has an interesting theory about weather cycles. According to his theory, the "new" pattern sets up every year in Sept-Oct...therefore the cool summer doesn't really predict anything for the winter. According to him, this cool summer was predicted by what happened last winter.